Quaternary groundwater history in south eastern Australia: Lake Sunrise, NSW

The Murray-Darling Basin of south-eastern Australia contains a trove of rich paleoenvironmental relicts, representing the unique hydroclimatic conditions under which they formed. Lake systems contain sediment archives of depositional history in their nearshore and bordering dune (lunette) geomorphic landforms. Fluctuating periods of high lake levels with intermittent periods of deflation (and subsequent dune building) can be interpreted from the high-resolution stratigraphy preserved within these landforms. An ephemeral groundwater discharge lake, known as Lake Sunrise, lacking major fluvial connectivity, was chosen for this study. Nearby lake basins, such as the Willandra Lakes complex, rely on fluvial inflows, as well as groundwater fluctuations to produce 'lake full' conditions, however this relationship is poorly understood. By contrast, due to its isolation, Lake Sunrise responds to fluctuations in the regional groundwater table. A stratigraphic framework based on particle size, mineralogy, and single-grain optically stimulated luminescence (OSL) age estimates was developed. A series of clay lunettes was analysed, revealing oscillating periods of enhanced groundwater discharge throughout the late Quaternary, from ~ 90 ± 4 ka - 24 ± 1 ka. Comparing these findings to other regional proxies reveal that groundwater discharge basins experience a ~10,000 – 20,000 year 'lag' between regional groundwater recharge and surface discharge.